Lighting assembly

ABSTRACT

A lighting fixture for facilitating plant growth and a light emitting component. The fixture includes a single light emission source LED device which provides at least two emission peaks in the wavelength range of 300-800 nm and at least one of the emission peaks has Full Width of Half Maximum (FWHM) at least 50 nm or higher. The emission peaks of the LED match well with a plant photosynthesis response spectrum and is therefore particularly suitable for high efficiency artificial lighting.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the use of LEDs in horticulturallighting applications. In particular, the present invention concerns alighting fixture for facilitating plant growth comprising at least oneLight Emitting Diode (LED) having spectral characteristics including apeak in the wavelength range from 600 to 700 nm. The present inventionalso concerns novel light emitting components which are particularlysuitable for facilitating plant growth and comprising a light emittingcompound semiconductor chip.

2. Description of Related Art

On the Earth the sun is the main source of visible (i.e. light) andinvisible electromagnetic radiation and the main factor responsible forthe existence of life. The net daily average solar energy reaching theEarth is approximately 28×10^23 J (i.e. 265 EBtu). This value is 5500times higher than the world's annual primary energy consumption,estimated in 2007 to be 479 PBtu. The spectral distribution of the sun'sradiation, as it can be measured at the earth's surface, has a broadwavelength band of between around 300 nm and 1000 nm.

However, only 50% of the radiation reaching the surface isphotosynthetically active radiation (PAR). PAR, according to the CIE(Commission Internationale de L'Eclairage) recommendations comprises thewavelength region of between 400 nm and 700 nm of the electromagneticspectrum. The laws of photochemistry can generally express the way thatplants harvest radiation. The dual character of radiation makes itbehave as an electromagnetic wave when propagating in space and asparticles (i.e. photon or quantum of radiant energy) when interactingwith matter. The photoreceptors are the active elements existing mainlyon plant's leaves responsible for the photon capture and for conversionof its energy into chemical energy.

Due to the photochemical nature of photosynthesis, the photosyntheticrate, which represents the amount of O₂ evolution or the amount of CO₂fixation per unit time, correlates well with the number of photonsfalling per unit area per second on a leaf surface. Therefore, therecommended quantities for PAR are based on the quantum system and areexpressed using the number of moles (mol) or micromoles (umol) ofphotons. The recommended term to report and quantify instantaneousmeasurements of PAR is the photosynthetic photon flux density (PPFD),and is typically expressed in μmoles/m²/s. This gives the number ofmoles of photons falling at a surface per unit area per unit time. Theterm photosynthetic photon flux (PPF) is also frequently used to referto the same quantity.

Photoreceptors existing in living organisms such as plants use theradiant energy captured to mediate important biologic processes. Thismediation or interaction can take place in a variety of ways.Photosynthesis together with photoperiodism, phototropism andphotomorphogenesis are the four representative processes related tointeraction between radiation and plants. The following expression showsthe simplified chemical equation of photosynthesis:6H₂O+6CO₂(+photon energy)→C₆H₁₂O₆+6O₂

As will appear from the equation, carbohydrates, such as sugar glucose(C₆H₁₂O₆), and oxygen (O₂), are the main products of the photosynthesisprocess. These are synthesized from carbon dioxide (CO₂) and water (H₂O)using the energy of the photons harnessed by using specialisedphotoreceptors such as chlorophylls and converted into chemical energy.

Through photosynthesis, the radiant energy is also used as the primarysource of chemical energy, which is important for the growth anddevelopment of plants. Naturally, the input-output reactant balance ofthe equation is also dependent on the quantity (i.e. number of photons)and quality (i.e. energy of the photons) of the radiant energy and,consequently, also of the produced biomass of the plants.“Photoperiodism” refers to the ability that plants have to sense andmeasure the periodicity of radiation, phototropism to the growthmovement of the plant towards and away from the radiation, andphotomorphogenesis to the change in form in response to the quality andquantity of radiation.

The typical absorption spectra of the most common photosynthetic andphotomorphogenetic photoreceptors, such as chlorophyll a, chlorophyll band betacarotene, and the two interconvertable forms of phytochromes(Pfr and Pr) are presented in FIG. 1.

The photomorphogenetic responses, contrary to photosynthesis, can beachieved with extremely low light quantities. The different types ofphotosynthetic and photomorphogenetic photoreceptors can be grouped inat least three known photosystems:photosynthetic, phytochrome andcryptochrome or blue/UV-A (ultraviolet-A).

In the photosynthetic photosystem, the existing pigments arechlorophylls and carotenoids. Chlorophylls are located in thechloroplasts' thylakoids located in the leaf mesophyll cells of plants.The quantity or the energy of the radiation is the most significantaspect, since the activity of those pigments is closely related to thelight harvest. The two most important absorption peaks of chlorophyllare located in the red and blue regions from 625 to 675 nm and from 425to 475 nm, respectively. Additionally, there are also other localizedpeaks at near-UV (300-400 nm) and in the far-red region (700-800 nm).Carotenoids such as xanthophylls and carotenes are located in thechromoplast plastid organelles on plant cells and absorb mainly in theblue region.

The phytochrome photosystem includes the two interconvertable forms ofphytochromes, Pr and Pfr, which have their sensitivity peaks in the redat 660 nm and in the far-red at 730 nm, respectively. Photomorphogeneticresponses mediated by phytochromes are usually related to the sensing ofthe light quality through the red (R) to far-red (FR) ratio (R/FR). Theimportance of phytochromes can be evaluated by the differentphysiological responses where they are involved, such as leaf expansion,neighbour perception, shade avoidance, stem elongation, seed germinationand flowering induction. Although shade-avoidance response is usuallycontrolled by phytochromes through the sensing of R/FR ratio, theblue-light and PAR level is also involved in the related adaptivemorphological responses.

Blue- and UV-A (ultraviolet A)-sensitive photoreceptors are found in thecryptochrome photosystem. Blue light absorbing pigments include bothcryptochrome and phototropins. They are involved in several differenttasks, such as monitoring the quality, quantity, direction andperiodicity of the light. The different groups of blue- andUV-A-sensitive photoreceptors mediate important morphological responsessuch as endogenous rhythms, organ orientation, stem elongation andstomatal opening, germination, leaf expansion, root growth andphototropism. Phototropins regulate the pigment content and thepositioning of photosynthetic organs and organelles in order to optimizethe light harvest and photoinhibition. As with exposure to continuousfar-red radiation, blue light also promotes flowering through themediation of cryptochromes photoreceptors. Moreover,blue-light-sensitive photoreceptors (e.g. flavins and carotenoids) arealso sensitive to the near-ultraviolet radiation, where a localizedsensitivity peak can be found at around 370 nm. Cryptochromes are notonly common to all plant species. Cryptochromes mediate a variety oflight responses, including the entrainment of the circadian rhythms inflowering plants such as the Arabidopsis. Although radiation ofwavelengths below 300 nm can be highly harmful to the chemical bonds ofmolecules and to DNA structure, plants absorb radiation in this regionalso. The quality of radiation within the PAR region may be important toreduce the destructive effects of UV radiation. These photoreceptors arethe most investigated and therefore their role in control ofphotosynthesis and growth is known reasonably well. However, there isevidence of the existence of other photoreceptors, the activity of whichmay have an important role in mediating important physiologicalresponses in the plant. Additionally, the interaction and the nature ofinterdependence between certain groups of receptors are not wellunderstood.

Photosynthesis is perhaps one of the oldest, most common and mostimportant biochemical process in the world. The use of artificial lightto substitute or compensate the low availability of daylight is a commonpractice, especially in northern countries during the winter season, forproduction of vegetable and ornamental crops.

The time of artificial electric lighting started with the development byThomas Edison in 1879 of Edison's bulb, commonly known today as theincandescent lamp. Due to its thermal characteristic, incandescence ischaracterised by a large amount of farred emission, which can reachapproximately 60% of the total PAR. In spite of the developments thathave taken place over more than a century, the electrical efficiency ofincandescent lamps, given by the conversion efficiency betweenelectrical energy consumed (input) and optical energy emitted (output)within the visible spectral region, is still very poor. Typically it isaround 10%. Incandescent light sources suffer also low lifetimeperformances, typically lifetime is not longer than 1000 hours. Inplant-growth applications their use is limited.

Growth of ornamental plants is one of the applications whereincandescent lamps can still be used. Floral initiation can be achievedwith long day responsive species using overnight exposure to low photonfluence rates using incandescent lamps. The high amount of far-redradiation emitted is used to control the photomorphogenetic responsesthroughout the mediation of the phytochromes.

Fluorescent lamps are more commonly utilized in plant-growthapplications than incandescent lamps. The electro-optical energyconversion is more efficient in comparison to incandescent lamps.Tubular type fluorescent lamps can achieve electrical efficiency valuesfrom typically around 20% to 30%, where more than 90% of the emittedphotons are inside the PAR region with typical lifetimes of around 10000hours. However, especially designed long-lifetime fluorescent lamps canreach lifetimes of between 30000 hours. Besides their reasonable energyefficiency and lifetime, another advantage of fluorescent lamps in plantgrowth is the amount of blue radiation emitted. This can reach more than10% of the total photon emission inside PAR, depending on the correlatedcolour temperature (CCT) of the lamp. For this reason, fluorescent lampsare frequently used for total substitution of natural daylight radiationin close growth rooms and chambers. The blue radiation emitted isindispensable to achieve a balanced morphology of most crop plantsthrough the mediation of the cryptochrome family of photoreceptors.

The metal halide lamp belongs to the group of high-intensity dischargelamps. The emission of visible radiation is based on the luminescenteffect. The inclusion of metal halides during manufacture allows to acertain extent the optimization of the spectral quality of the radiationemitted. Metal halide lamps can be used in plant growth to totallyreplace daylight or for partially supplementing it during the period oflower availability. The high PAR output per lamp, the relatively highpercentage of blue radiation around 20% and the electrical efficiency ofapproximately 25%, makes metal halide lamps an option for year-roundcrop cultivation. Their operation times are typically 5,000 to 6,000hours. The high-pressure sodium (HPS) lamp has been the preferred lightsource for year-round crop production in greenhouses. The main reasonshave been the high radiant emission, low price, long life time, high PARemission and high electrical efficiency. These factors have allowed theuse of high-pressure sodium lamps as supplemental lighting sourcessupporting vegetative growth in a cost-effective way during wintertimein northern latitudes.

However, the spectral quality in HPSs lamps is not optimal for promotingphotosynthesis and photomorphogenesis, resulting in excessive leaf andstem elongation. This is due to the unbalanced spectral emission inrelation to the absorption peaks of important photosynthetic pigmentssuch as chlorophyll a, chlorophyll b and betacarotene. The low R/FRratio and low blue light emission in comparison with other sourcesinduces excessive stem elongation to most of the crops grown under HPSlighting. Electrical efficiencies of high-pressure sodium lamps aretypically within 30% and 40%, which make them the most energy-efficientlight sources used nowadays in plant growth. Approximately 40% of theinput energy is converted into photons inside the PAR region and almost25% to 30% into far-red and infra red. The operation times of highpressure sodium lamps are in the range from about 10,000 to 24,000hours.

The low availability of daylight in northern latitudes and the demand ofconsumers for quality horticultural products at affordable pricesyear-round set demands for new lighting and biological technologies.Also production yields globally can be significantly increased ifdaylight is available up 20 to 24 hours per day. Therefore, approachesthat can reduce production costs, increase yields and quality of thecrops are needed. Lighting is just one of the aspects involved that canbe optimized. However, its importance cannot be underestimated. Theincrease in electricity prices and the need to reduce CO₂ emissions areadditional reasons to make efficient use of energy. In year-round cropproduction in greenhouses, the electricity cost contribution to overheadcosts may reach in some crops approximately 30%.

Although existing light sources commonly used for plant growth may haveelectrical efficiencies close to 40%, the overall system efficiency(i.e. including losses in drivers, reflectors and optics) can besignificantly lower. The spectral quality of the radiation plays animportant role in the healthy growth of the crop. The conventional lightsources cannot be spectrally controlled during its utilization withoutthe inefficient and limited utilization of additional filters. Moreover,the control of the radiation quantity is also limited, reducing thepossibility of versatile lighting regimes such as pulsed operation.

Therefore, and for reasons relating to the previously described aspects,the light-emitting diode and related solid-state lighting (SSL) haveemerged as potentially viable and promising tools to be used inhorticultural lighting. Internal quantum efficiency of LEDs is a measurefor the percentage of photons generated by each electron injected intothe active region. In fact, the best AlInGaP red and AlInGaN green andblue HB-LEDs can have internal quantum efficiencies better than 50%;still challenges remain to extract all generated light out of thesemiconductor device and the light fixture.

In horticultural lighting the main practical advantages of LED-basedlight sources in relation to conventional light sources is thedirectionality and full controllability of the emitted radiation. LEDsdo not necessarily require reflectors, as they are naturallyhalfisotropic emitters. LEDs as directional emitters avoid most of thelosses associated with the optics. Additionally, the narrow spectralbandwidth characteristic of coloured LEDs is another important advantagein relation to conventional broad waveband light sources. The mainadvantage of using LEDs as photosynthetic radiation sources results fromthe possibility of selecting the peak wavelength emission that mostclosely matches the absorption peak of a selected photoreceptor. Infact, this possibility brings with it additional advantages. Theefficient usage of the radiant energy by the photoreceptor on themediation of a physiological response of the plant is one of theadvantages. Another advantage is the controllability of the response byfully controlling the radiation intensity.

The advantages mentioned previously can be further extended to theluminaire level. The inventor is aware of a luminaire with a blue LEDand a red LED. The spectral emission of currently coloured AlInGaN LEDsare available from UV into to the green region of the visible spectrum.Those devices can emit in the blue and UV-A region where the absorptionpeaks of cryptochromes and carotenoids are located.

Chlorophyll a and the red isomeric form of phytochromes (Pr) have astrong absorption peak located around 660 nm. AlGaAs LEDs emit in thesame region but, partially due to low market demand and outdatedtechnology of production, they are expensive devices if compared withphosphide or even nitride-based LEDs. AlGaAs LEDs can be also used tocontrol the far-red form of phytochromes (Pfr), which has an importantabsorption peak at 730 nm.

AlInGaP LEDs are based on a well-established material technology withthe relatively high optical and electrical performance. Typically, thecharacteristic spectral emission region of AlInGaP red LEDs covers theregion where chlorophyll b has its absorption peak, around 640 nm.Therefore, AlInGaP LEDs are also useful in promoting photosynthesis.

The novel commercial high brightness LEDs are not suitable forgreenhouse cultivation as their main emission peak lies in the range ofgreen wavelengths extending from 500 to 600 nm and thus not respondingto photosynthesis process. However, in principal according to the art aLED light to which the photosynthesis responds can be constructedcombining various types of semiconductor LEDs such as AlInGaP andAlInGaN, for red and blue colors.

There are a number of problems related to the combination ofindividually colored LEDs. Thus, different types of semiconductordevices will age at different rates and for this reason the ratio of redcolour to blue color will vary over time, resulting further inabnormalities in a plant growth process. A second major issue is thatindividual single color LEDs have relatively narrow spectral coverage,typically less than 25 nm, which is insufficient for providing goodphotosynthesis efficiency without utilizing very high number ofdifferent color and individual LEDs and causing high cost ofimplementation.

It is known from EP 2056364 A1 and US 2009/0231832 that an enhancednumber of colors can be generated from LEDs using wavelength conversionmaterials, such as phosphor, to re-emit different colors of light.Allegedly, the different colors replicating sunlight can be used totreat depression or seasonal disease according to US 2009/0231832. Thesedocuments are cited here as reference.

These lights have many disadvantages, even if they were to be used ashorticultural lights, for example due to the simple reason that thespectrum of sunlight is suboptimal for plant growth. The light of US2009/0231832 that aims to replicate sunlight contains many superfluouswavelengths that are not used efficiently by plants in their growth. Forexample the band of 500-600 nm (green light) is poorly used by plants asgreen plants reflect this wavelength. This leads to wasted energy inhorticultural applications.

Furthermore, the lights of the prior art also omit essentialwavelengths, which would be very useful for plant growth. For example,these lights do not reach to far red between 700 nm-800 nm, which isimportant to plant cultivation.

SUMMARY OF THE INVENTION

It is an aim of the present invention to eliminate at least a part ofthe problems relating to the art and to provide a new way offacilitating plant growth using LEDs.

It is a first objective of the invention to provide a single lightemission source based LED device to which the photosynthesis processresponds well.

It is a second objective of the invention to provide a lighting fixturefor greenhouse cultivation based on a photosynthesis photon flux (PPF)optimized LED device.

It is a third objective of the invention to achieve an LED device thatprovides at least two emission peaks in the wavelength range from 300 to800 nm and at least one of the emission peaks has Full Width of HalfMaximum (FWHM) of at least 50 nm or more.

It is a fourth objective of the invention to provide LED basedgreenhouse cultivation lighting fixture wherein the emission intensityratio of two emission frequencies, 300-500 nm and 600-800 nm, arereduced with less than 20% during the 10,000 hours of operation.

It is a fifth objective of the invention to provide a technical solutiongiving a better PPF value per Watt (i.e. PPFs against used powerwattage) than attained by a conventional high pressure sodium lampnormally used in greenhouse cultivation and thus providing an energyefficient light source for greenhouse cultivation process and artificiallighting used therein.

It is a sixth objective of the invention to provide a single lightemission source wherein the emission at a frequency of 300-500 nm isgenerated by the semiconductor LED chip and the emission at a frequencyof 600-800 nm is generated using a partial wavelength up-conversion ofthe LED chip radiation power. The inventor has discovered that forexample cucumber and lettuce plants reach greater length and/or masswhen illuminated with the inventive horticultural light that includesfar red light (700-800 nm).

It is a seventh objective of the invention to provide a single lightemission source where the emission at frequency of 300-500 nm isgenerated by the semiconductor LED chip and the emission at frequency of600-800 nm is generated using a partial wavelength up-conversion of theLED chip radiation power. The wavelength up-conversion to produce600-800 nm radiation is achieved by using one or more wavelengthup-conversion materials in proximity with the LED emission source.

In this application “up-conversion” is construed as changing thewavelength of incoming absorbed light to emitted light of longerwavelengths.

It is an eighth objective of the invention to provide 400-500 nm,600-800 nm or both frequency ranges partial or complete wavelengthup-conversion of semiconductor LED chip radiation, the chip havingemission at 300-500 nm range emission range. The wavelengthup-conversion is realized by using either organic, inorganic orcombination of both types of materials.

It is a ninth objective of the invention to provide the wavelengthup-conversion using nano-sized particle material for the up-conversion.

It is a tenth objective of the invention to provide the wavelengthup-conversion using molecular like material for the up-conversion.

It is an eleventh objective of the invention to provide the wavelengthup-conversion using a polymeric material wherein the up-conversionmaterial is covalently bonded to the polymer matrix providing thewavelength up-conversion.

It is a twelfth objective of the invention to present a LED basedlighting fixture where the spectral band 500-600 nm is suppressed. Inthis suppressed band there is hardly any or no emission at all, or inany case less emission than in either of the adjacent bands 400-500 nm,600-700 nm. The suppression can be achieved in accordance with theinvention by not having any or only a small amount of primary emissionin the band 400-500 nm, and by making sure that any up-conversion causesa wavelength shift that shifts the wavelength beyond 600 nm. It isgenerally known that green plants can not utilize green light (500-600nm) radiation as well as the radiation in the adjacent bands, as thisradiation merely reflects from the plant rather than is being absorbedfor photosynthetic conversion.

It is a thirteenth objective of the invention to present a LED basedlighting fixture that maximizes anabolic growth of plants by providingdesired far-red light, whereas it minimizes green light which from theperspective of plant cultivation is radiation that wastes energy. Thisobjective is realized in one aspect of the invention by a blue LED witha wavelength up-conversion device which up-converts part of the emittedblue light (300-500) nm into a broad red spectrum component (600-800 nm)which has a far-red component, but omits and/or minimizes the greencomponent (500-600 nm).

The present invention provides a light emitting diode and a relatedlight fixture suitable for greenhouse cultivation. According to theinvention, the light emitting diode has a specific emission frequencypattern, viz. it has at least two spectral characteristics; one emissionpeak with a full width of half maximum of at least 50 nm or more andhaving a peak wavelength in the range of 600 to 700 nm, and a secondspectral characteristics having a peak wavelength below 500 nm range.The emission peaks of the LED match well with a plant photosynthesisresponse spectrum and is therefore particularly suitable for highefficiency artificial lighting.

A light emitting component suitable for facilitating plant growth,comprises a light emitting compound semiconductor chip; and a lightwavelength up-conversion phosphor which is deposited in direct proximityof the LED chip. Such a component is capable of emitting twocharacteristic light emission peaks.

More specifically, the light fixture according to the invention ischaracterized by what is stated in the characterizing part of claim 1and/or 2.

A lighting fixture for facilitating plant growth in accordance with theinvention comprises at least one Light Emitting Diode (LED) having

a) first spectral characteristics including a peak in the wavelengthrange from 600 to 700 nm and arranged to exhibit a full width of halfmaximum of at least 50 nm or more; and

b) second spectral characteristics with a maximum of 50 nm full width ofhalf maximum and arranged to exhibit a peak wavelength in the range from440 to 500 nm.

A horticultural lighting fixture in accordance with the inventioncomprises at least one Light Emitting Diode (LED) having

a) first spectral characteristics including a peak in the wavelengthrange from 600 to 700 nm and arranged to exhibit a full width of halfmaximum of at least 50 nm or more;

b) second spectral characteristics with a maximum of 50 nm full width ofhalf maximum and arranged to exhibit a peak wavelength in the range from440 to 500 nm, and

c) all or part of the emission at a frequency of 600-800 nm is generatedusing a whole or partial wavelength up-conversion of the LED chipradiation power.

A horticultural lighting fixture in accordance with the inventioncomprises at least one Light Emitting Diode (LED) having

a) first spectral characteristics including a peak in the wavelengthrange from 600 to 700 nm and arranged to exhibit a full width of halfmaximum of at least 50 nm or more;

b) second spectral characteristics with a maximum of 50 nm full width ofhalf maximum and arranged to exhibit a peak wavelength in the range from440 to 500 nm, and

c) at least a part or the whole of the emission at wavelengths of500-600 nm is arranged to be minimized and/or omitted and/or to bereduced below the intensity in 400-500 nm band and below the intensityin 600-700 nm band.

A lighting fixture for facilitating plant growth in accordance with theinvention comprises a luminescent UV LED, optionally with externalemission characteristics, said LED arranged to exhibit

a) first phosphorescent spectral characteristics with a peak wavelengthin the range of 350 to 550 nm;

b) second optional phosphorescent spectral characteristics with a peakwavelength in the range of 600 to 800 nm;

c) third optional phosphorescent spectral characteristics with a peakwavelength freely adjustable between 350 and 800 nm;

d) the phosphorescent emission intensities of first, optional second andoptional third spectral characteristics being adjustable in any ratio.

The light emitting component is characterized by what is stated in thecharacterizing part of claim 16 and/or 17.

A light emitting component for facilitating plant growth in accordancewith the invention, comprises;

-   -   a light emitting compound semiconductor chip; and    -   a light wavelength up-conversion phosphor which is deposited in        direct proximity of the LED chip; said component being capable        of emitting two characteristic light emission peaks.

A light emitting component of a horticultural light in accordance withthe invention comprises;

-   -   a light emitting compound semiconductor chip; and    -   a light wavelength up-conversion phosphor which is deposited in        direct proximity of the LED chip;        said component being capable of emitting two characteristic        light emission peaks, and all or part of the emission at a        frequency of 600-800 nm is generated using a whole or partial        wavelength up-conversion of the LED chip radiation power.

A light emitting component of a horticultural light in accordance withthe invention comprises;

-   -   a light emitting compound semiconductor chip; and    -   a light wavelength up-conversion phosphor which is deposited in        direct proximity of the LED chip;        said component being capable of emitting two characteristic        light emission peaks, and at least a part or the whole of the        emission at wavelengths of 500-600 nm is arranged to be        minimized and/or omitted and/or to be reduced below the        intensity in 400-500 nm band and below the intensity in 600-700        nm band.

The best mode of the invention is considered to involve a plurality ofLEDs in the wavelength range of 380-850 nm arranged with emissionspectra that is arranged to coincide with the photosynthetic response ofa plant to be cultivated with the lighting of the said LEDs. The bestmode will feature wavelength up-conversion by phosphor from blue LEDemission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows relative absorption spectra of the most commonphotosynthetic and photomorphogenetic photoreceptors in green plants;

FIG. 2 shows the emission peaks of a first single light emission sourceLED device according to the invention;

FIG. 3 shows the emission peaks of a second single light emission sourceLED device according to the invention;

FIG. 4 shows the emission peaks of a third single light emission sourceLED device according to the invention;

FIG. 5 shows the emission peaks of a fourth single light emission sourceLED device according to the invention; and

FIGS. 6a to 6c show in a schematical fashion the various process stepsof a method of producing a modified LED device according to a preferredembodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As already discussed above, the present invention relates in general toa single light emission source LED device that has optimal properties tobe used as greenhouse cultivation light source. Specifically thisapproach to construct the light sources has optimal properties andflexibility for matching the photosynthesis frequencies in plantcultivation. By using this approach, the light sources can be designedto reach superior PPF and PPF per watt efficiency and performance andvery low power consumption and very long operation lifetime whencompared to the existing technologies.

In particular the single light emission source LED device provides atleast two emission peaks in the wavelength range of 300-800 nm and atleast one of the emission peaks has Full Width of Half Maximum (FWHM) atleast 50 nm or higher. The emission peaks and relative intensities areselected to match the photosynthesis frequencies for the plant. Also therequired PPF quantity for the light source is optimized to meet theplant requirement.

The emission at a frequency of 300-500 nm is generated by thesemiconductor LED chip and the emission at frequency of 400-800 nm isgenerated using a complete or partial wavelength up-conversion of theLED chip radiation power. The partial wavelength up-conversion can beselected to be in range of 5-95%, preferably 35-65%, of thesemiconductor LED chip radiation. The wavelength up-conversion toproduce the 400-800 nm radiation is achieved by using one or moreup-conversion materials in proximity with the LED emission source. Thewavelength up-conversion is realized by using either organic, inorganicor combination of both types of materials. These materials can beparticular (nano- or other size particles), molecular or polymericmaterials. Furthermore the materials can have structural arrangementthat results in wavelength up-conversion of the emission source.

According to one particular embodiment, a lighting fixture forfacilitating plant growth comprises a UV LED, optionally with externalluminescent emission characteristics. The LED exhibits typically

a) first phosphorescent spectral characteristics with a peak wavelengthin the range of 350 to 550 nm;

b) second optional phosphorescent spectral characteristics with a peakwavelength in the range of 600 to 800 nm; and

c) third optional phosphorescent spectral characteristics with a peakwavelength freely adjustable between 350 and 800 nm.

In this application “adjustable” peak wavelength as in the above isconstrued as a peak wavelength that can be adjusted during assembly ofthe lighting fixture at the factory, and/or also “adjustable” as in anadjustable dial in the lighting fixture for on site peak wavelengthadjustment. In addition adjusting the peak wavelengths of the LED duringmanufacturing process of the LED is also in accordance with theinvention, and “adjustable” should be construed to also includeadjustments made during the manufacturing process of the LED. Allaforementioned embodiments of an adjustable peak wavelength, or anyother adjustable light source or LED variable are within the scope ofthis patent application.

Preferably the phosphorescent emission intensities of first, optionalsecond and optional third spectral characteristics are adjustable in anyratio.

FIGS. 2 to 5 illustrate a few examples of the emission peaks of thesingle light emission source LED devices.

In FIG. 2, the semiconductor LED chip emission frequency peaks at awavelength of 457 nm with emission peaks Full Width of Half Maximum(FWHM) of 25 nm. In this case the wavelength up-conversion is done byusing two up-conversion materials. These two wavelength up-conversionmaterials have individual emission peaks at 660 nm and 604 nm. FIG. 2shows the combined emission peak from these two wavelength up-conversionmaterials peaking at 651 nm wavelength with emission peaks FWHM of 101nm. In this case about 40% (calculated from the peak intensities) of thesemiconductor LED chip emission, is up-converted to 651 nm emission bytwo individual up-conversion materials.

In FIG. 3, the semiconductor LED chip emission frequency peaks at awavelength of 470 nm with emission peaks Full Width of Half Maximum(FWHM) of 30 nm. In this case the wavelength up-conversion is done byusing two up-conversion materials. These two wavelength up-conversionmaterials have individual emission peaks at 660 nm and 604 nm. FIG. 2shows the combined emission peak from these two wavelength up-conversionmaterials peaking at 660 nm wavelength with emission peaks FWHM of 105nm. In this case about 60% (calculated from the peak intensities) of thesemiconductor LED chip emission, is up-converted to 660 nm emission bytwo individual “up-conversion” materials.

In FIG. 4, the semiconductor LED chip emission frequency peaks at awavelength of 452 nm with emission peaks Full Width of Half Maximum(FWHM) of 25 nm (not shown in the figure). In this case the wavelengthup-conversion is done by using one up-conversion material. FIG. 3 showsthe emission peak from this up-conversion material peaking at 658 nmwavelength with emission peaks FWHM of 80 nm. In this case about 100%(calculated from the peak intensities) of the semiconductor LED chipemission, is up-converted to 658 nm emission by the up-conversionmaterial. This can be noticed from the FIG. 4, as there are no 452 nmemission exiting the LED device.

In FIG. 5, the semiconductor LED chip emission frequency peaks at awavelength of 452 nm wavelength with emission peaks Full Width of HalfMaximum (FWHM) of 25 nm. In this case the wavelength up-conversion isdone by using one up-conversion material. FIG. 5 shows the emission peakfrom this up-conversion material peaking at 602 nm wavelength withemission peaks FWHM of 78 nm. In this case about 95% (calculated fromthe peak intensities) of the semiconductor LED chip emission, isup-converted to 602 nm emission by the wavelength up-conversionmaterial.

For the above mentioned spectrum the device can be constructed asexplained in details below. The semiconductor LED chip emissionfrequency should be selected the way that it is suitable for excitingthe used phosphor molecules in the device. The emission from the LEDchip can be between 400 nm and 470 nm.

The used phosphor molecule or molecules should be selected the way thata desired emission spectra from the LED is achieved.

In the following we will describe a procedure for using two phosphormaterials (wavelength up-conversion materials) in the LED device toachieve the desired spectra (cf. FIGS. 6a to 6c ).

Phosphor A and Phosphor B are mixed in a pre-determined ratio to achievedesired phosphor emission spectra from the LED device (cf. FIG. 6a ).The ratio of the phosphors can be for example 99:1 (A:B) to 1:99. Thismixture of phosphors A+B is mixed into a material C (for example apolymer) at a pre-determined concentration to form an “encapsulant”. Theconcentration of the phosphors in material C can be for example 99:1(phosphor mixture:material C) to 1:99. This mixture of materialC+phosphors (A and B) is then deposited in direct proximity of the LEDchip (FIGS. 6b and 6c ). By “proximity” we mean it can be depositeddirectly on the surface of the LED chip or spaced out with other opticalmaterial. The concentration of the phosphor mixture in material Cdetermines the wavelength up-conversion amount of the semiconductor LEDchip emission frequency, meaning how much of the “original” LED chipemission frequency is seen in the final LED device emission and how muchis converted into the phosphor emission in the LED device.

The thickness of the encapsulant (into which the phosphor is mixed)typically varies from 0.1 um to 20 mm, in particular 1 um to 10 mm,preferably 5 um to 10 mm, for example about 10 um to 5 mm, depending onthe concentration of the phosphor.

Typically the concentration of the phosphor (calculated from the totalweight of the encapsulant) is about 0.1 to 20%, preferably about 1 to10%.

The wavelength up-conversion can be 100%, meaning that there is onlyphosphor emission seen from the LED device or it can be less than 100%,meaning that some of the LED chip emission is transmitted out from theLED device.

To summarize, by tuning the phosphor ratio A:B it is possible to tunethe desired phosphor emission spectra from the LED device and by tuningthe phosphor concentration in material C it is possible to tune thedesired LED chip emission quantity/amount for the LED device.

The amount (physical thickness) of material C (with certain phosphorconcentration) on top of the LED chip also affects the amount of LEDchip emission transmitting from the LED device. The thicker the materialC layer on top of the LED chip, the lower the transmission.

Material C can be for example a solvent, inorganic or organic polymer,silicon polymer, siloxane polymer or other polymer where the phosphorcan be mixed into. Material C can have one or more components that haveto be mixed prior to usage together with the phosphor. Material C can bea thermally or UV curable material.

The mixture of the phosphor(s) and the solvent material C (solid orliquid) can be translucent or transparent, preferably transparent, toallow for passage of the light emitted from the LED.

In one embodiment that is especially preferable the far red radiation(700-800 nm) is produced by for example europium-cerium co-doped Ba_xSr_y ZnS_3 phosphors and/or cerium doped lanthanide oxide sulfides.These phosphor and sulfide types have emission peak maxima between650-700 nm wavelength region and exhibit also broad (50-200 nm) fullwidth of half maximum and therefore also produce light emission athigher wavelength, i.e., above 700 nm wavelength range.

In addition to or as an alternative to using phosphors or other similarmaterials it is also possible to realize the wavelength up-conversion bymeans of at least one semiconductor quantum dot or the like, which isplaced near the LED.

Example

A LED lighting fixture was constructed for comparison testing purposesbased on the single LED device having identical output spectrum of theFIG. 3. The lighting fixture consisted of 60 individual LED units havinga power consumption of 69 W which includes the power consumption of theAC/DC constant current driver.

The comparison devices were commercial HPS (High Pressure Sodium) lampgreenhouse lighting fixture with total power consumption of 420 W andcommercial LED greenhouse LED fixture. The commercial LED fixture wasbased on individual blue and red LED devices having total powerconsumption of 24 W.

The LED lighting fixture according to the present invention was testedagainst the above-mentioned commercial LED devices using following PPFmeasurement procedure and arrangement.

PAR irradiance (irradiance value between 400 nm and 700 nm) andPPF-values were calculated by measuring the light fixture spectra from300 nm to 800 nm and absolute irradiance value at band from 385 nm to715 nm. The spectrum of each lamp were measured with ILT700Aspectroradiometer at one distance. The absolute irradiance-values weremeasured with precision pyranometer at certain distances and were laterused to calculate the absolute spectra to these distances. Theseabsolute spectra were used to calculate PAR- and PPF calculations.PAR-irradiance (W/m²) was calculated by integrating the absolutespectrum from 400 nm to 700 nm. PPF-values were calculated by firsttranslating the irradiance value of each “channel” of the spectrum fromW/m² to microeinsteins and then integrating this spectrum over thedesired wavelength band.

The comparison result of these two commercial greenhouse lamp fixturesand the LED fixture according to the innovation are presented in thetable below. The results are also normalized against the commercial HPSlighting fixture.

Type HPS Ref. Grow LED LED of Invention Power (W) 420 24 69 Total PPF164 26 88 PPF/Watt 0.39 1.08 1.28 PPF efficiency 1 2.77 3.27 normalizedto Ref. HPS PPF efficiency 100% 277% 327% normalized to Ref. HPS (%)

As will appear from the test results shown, an LED lighting fixtureaccording to the present invention provides 3.27 times higher PPFefficiency compared to HPS and 1.18 times better PPF efficiency comparedto commercial LED greenhouse fixture based on individual blue and redLED devices. Naturally all of the LEDs or lighting fixtures are arrangedto be used especially in greenhouses for plant cultivation as greenhouselights in many embodiments of the invention.

The above examples have described embodiments in which there is oneLight Emitting Diode (LED) having the indicated spectralcharacteristics. Naturally, the present lighting fixtures may comprise aplurality of LEDs, at least some (say 10% or more) or preferably amajority (more than 50%) of which have the indicated properties andcharacteristics. It is therefore possible to have fixtures comprisingcombinations of conventional LEDs and LEDs of the present kind There areno particular upper limits to the number of LEDs. Thus, lightingfixtures of the present kind can have roughly 1 up to 10,000 LEDs,typically 1 to 1000 LEDs, in particular 1 to 100 LEDs.

It is in accordance with the invention to include LEDs with differentpeak emissions in one luminaire and to control these in order to providea desirable spectral emission to achieve a determined growth result orphysiological response. In this way, the lighting system would allow aversatile control of lighting intensity and spectrum. Ultimately, thecontrol of other abiotic parameters such as CO₂ concentration,temperature, daylight availability and humidity could be integratedwithin the same control system together with lighting, optimizing thecrop productivity and the overall management of the greenhouse.

REFERENCES

-   EP 2056364 A1, Satou et al.-   US 2009/0231832, Zukauskas et al.

The invention claimed is:
 1. A horticultural light, comprising: at leasttwo Light Emitting Diodes (LEDs) emitting light including far red lightin a wavelength range from 700 nm-800 nm and reducing green light belowthe light intensity in each of the bands adjacent to the green light,the emitted light including spectral emission peaks matching carotenoidand chlorophyll absorption peaks, the at least two LEDs having firstspectral characteristics with maximum 50 nm full width of half maximumand a peak wavelength in a range of 400 to 500 nm; and at least oneadjustable dial configured to adjust at least one peak wavelength of thefirst spectral characteristics.
 2. The light of claim 1, wherein atleast a part or the whole of an emission at wavelengths of 500-600 nm isminimized and/or omitted and/or to be reduced below an intensity in a400-500 nm band and below the intensity in a 600-700 nm band.
 3. Thelight of claim 1, wherein the at least two LEDs have spectralcharacteristics with a freely adjustable peak in a wavelength range from500 to 800 nm and that exhibit at least 30 nm full width of halfmaximum.
 4. The light of claim 3, further comprising at least oneelectronic control system to switch first and the second LEDsindependently on and off or alternatively dim independently by 0-100%power.
 5. The light of claim 1, wherein emission intensities of spectralcharacteristics of the LEDs are adjustable.
 6. The light of claim 1,wherein the at least two LEDs are of a first type and a second type, aratio of LEDs of the first type to LEDs of the second type being 1 to100.
 7. The light of claim 1, wherein a photosynthetic photon flux (PPF)value of the light per Watt is 0.35 or higher.
 8. The light of claim 1,wherein an emission decay rate difference of first and second spectralcharacteristics amounts to less than 20% during a first 10,000 hoursusage, or during a first 25,000 hours usage.
 9. The light of claim 1,wherein spectral emission characteristics, intensity, peak wavelengthand full width of half maximum are controlled with selection andconcentration of phosphor material.
 10. The light of claim 1, whereinspectral emission characteristics, intensity, peak wavelength and fullwidth of half maximum are controlled with blue emission characteristicsof a LED chip.
 11. The light of claim 1, wherein the at least two LEDsinclude a first LED that has phosphorescent spectral characteristics ofa freely adjustable peak wavelength in the range of 500 nm to 800 nmrange that exhibit at least 30 nm full width of half maximum, and firstemission intensities of spectral characteristics adjustable in anyratio.
 12. The light of claim 11, wherein the at least two LEDs includea second LED with one or more luminescent spectral characteristics withmaximum 50 nm full width of half maximum and peak wavelength in therange of 400 to 500 nm, and optional phosphorescent spectralcharacteristics having freely adjustable peak wavelengths in the rangeof 450 nm to 800 nm.
 13. The light of claim 1, wherein an up-conversionof LED emission is established by one or more of at least onesemiconductor quantum dot, phosphor material, and sulfide material. 14.A light for facilitating plant growth, comprising: at least twoluminescent UV light emitting diodes (LEDs), with external emissioncharacteristics, the luminescent UV LEDs emitting light including farred light in a wavelength range from 700 nm-800 nm and reducing greenlight below the light intensity in each of the bands adjacent to thegreen light, the emitted light including spectral emission peaksmatching carotenoid and chlorophyll absorption peaks; and at least oneadjustable dial configured to adjust phosphorescent emission intensitiesof the emitted light from the at least two LEDs in any ratio toaccommodate plant growth, wherein the at least two LEDs have spectralcharacteristics with maximum 50 nm full width of half maximum and a peakwavelength in a range of 400 to 500 nm.
 15. A method for enhancing plantgrowth, comprising: the at least one light of claim 1 emitting light toat least one plant.
 16. The light of claim 1, wherein the at least twoLEDs have second and third spectral characteristics having freelyadjustable peak wavelengths in a range from 450 nm to 800 nm.
 17. Ahorticultural light, comprising: at least two Light Emitting Diodes(LEDs) emitting light including far red light in a wavelength range from700 nm-800 nm and reducing green light below the light intensity in eachof the bands adjacent to the green light, the emitted light includingspectral emission peaks matching carotenoid and chlorophyll absorptionpeaks, whcrcin the at least two LEDs having spectral characteristicswith maximum 50 nm full width of half maximum and a peak wavelength in arange of 400 to 500 nm; and at least one adjustable dial configured toadjust at least one peak wavelength of the spectral characteristics,wherein a wavelength up-conversion of radiation power of the LEDs isformed by at least two phosphor materials.